Separation of mixtures of biopolymers, in particular of DNA molecules of a size greater than 5.multidot.10.sup.4 nucleic base pairs is based on the pulse electrophoresis involving the consecutive creation of crossing electric fields in gel in which a mixture of high-molecular DNA is introduced.
Known in the art is an apparatus for separating mixtures of DNA molecules Carle GP (Frank M. and Olson M. V. Electrophoretic Separation of Large DNA molecules by "Periodic Inversion of the Electric Field". Science. v. 232. 1986, pp. 65-68), in which a rectangular horizontally extending electrophoretic chamber has two opposed linear electrodes between which a block of gel is placed. Voltage from a power supply is applied through a switching circuit to the electrodes during 3/4 of a preset time period in the direct polarity and during 1/4 of the same time period in the inverted polarity, and this switching cycle is repeated for a large number of times. Movement of DNA molecules is thus regularly reversed at 180.degree.. This angle is not an optimum angle for a large range of molecular mass values of DNA molecules being separated so that it is not possible to isolate individual fractions of DNA of a size greater than 2.multidot.10.sup.6 base pairs. In addition, reciprocations of molecules within the gel block result in an increase in the time of separation of the initial mixture or in a lower productivity of the apparatus.
Known in the art is an apparatus (G. Chy, D. Vollarth, R. W. Davis. Separation of Large DNA Molecules by Contour-Clamped Homogeneous Electric Fields. Science. v. 234. 1986. pp. 1582-1585), in which six groups of point-like electrodes extending vertically with respect to the surface of a gel block define a hexahedron which is electrically short-connected through identical resistors, the gel block being placed inside the hexahedron. Voltage from a constant polarity power supply is applied consecutively through a switching circuit to respective pairs of opposed groups of electrodes. A third pair of groups of electrodes remains passive and designed for creating a homogeneous electric field between the electrodes. DNA molecules move with a change in direction of movement at 120.degree. upon every switching of the voltage. With the same dimensions of the chamber as in the above described apparatus, the gel block should be of a smaller size, hence with a smaller number of samples thus lowering productivity of the apparatus. In addition, power output of the power supply should be doubled as current flowing through the electrodes should be at least equal to current flowing through buffer solution covering the gel block.
Known in the art is an apparatus for the separation of high-molecular weight DNA in a gel (U.S. Pat. No. 4,473,452) which makes it possible to separate mixtures of DNA molecules with molecular masses from 5.multidot.10.sup.4 to 9.multidot.10.sup.6 base pairs. A square-shaped electrophoretic chamber of the apparatus accommodates four groups of electrodes, groups of point-like electrodes being provided on two adjacent walls and electrically connected to each other within each group, and two individual point-like electrodes being provided on the other pair of adjacent walls of the chamber in the immediate vicinity to the ends of the two opposed groups of electrodes. Voltage of negative polarity is applied from a power supply source through a switching circuit during identical time intervals to one group of electrodes and voltage of positive polarity is applied, to the opposed point-like electrode. Subsequently voltage is applied in the same manner to the second group of electrodes and to the second individual electrode. Crossing curvilinear elecgric fields are thus created in the gel block placed in the electrophoretic chamber to cause DNA moleculaes to move along complex trajectories the direction of which changes within the range from 90.degree. to 180.degree. moving close to the point-like electrodes.
Curvilinear configuration of fields created in the prior art apparatus results, first, in a curvature of tracks of individual DNA fractions in the gel thus substantially hampering determination of their molecular mass and calls for the employment of special correcting programs for automatic processing of results, e.g. when gel scanners are used. Second, the number of concurrently separated DNA molecules is small as the end tracks are curved so that they may even come out of the gel into the buffer solution.